The present invention relates to magnetic heads, and more particularly, this invention relates to a mechanism integrated in the head itself for generating a magnetic field for testing the head.
Magnetoresistive heads are devices suitable for reading magnetically-recorded information, for example, information stored on a magnetic tape or disk. Magnetoresistive heads contain a material which has a resistance that varies as a function of the strength of the magnetic field applied to it. For such materials, if the resistance of the head in the absence of a magnetic field is R, the resistance of the material in the presence of a magnetic field of strength B will be some lower value Rxe2x88x92r. Generally, r, the function which expresses the dependence of the resistance of the material on the applied magnetic field, is a symmetric nonlinear function with an absolute maximum at the point B=0.
The resistive properties of a typical magnetoresistive device are illustrated in FIG. 1, which is an idealized graph of the resistance Rtotal of the device (on the vertical axis) as a function of the strength of the applied magnetic field B (on the horizontal axis). From FIG. 1, it can be seen that the resistance curve 10 includes a constant component R (defined as the maximum resistance of the device at the point about which the resistance curve 10 is symmetric) and a component r which varies as a function of the applied magnetic field. The total resistance, then, is Rtotal=Rxe2x88x92r(B), because the resistance Rtotal decreases around the point where R is measured as a function of the applied magnetic field.
Before a magnetoresistive head is employed to read magnetically-recorded information on a disk drive, a test of its resistive properties as a function of an applied magnetic field is usually performed to ensure quality control. Current magnetic head testers rely on external devices to generate magnetic fields, which are sensed by the read device in the head and react to field transitions. In particular, current testers subject the magnetic head to a fluctuating magnetic field generated by passing a controlled current through an appropriate winding (coils of electromagnets) of an external magnetic field generator.
This prior-art method for testing magnetoresistive heads suffers from several disadvantages. The first of these is that the frequency of operation of the tester is very limited. Due to problems with resistance and inductance in the electromagnets, there is no practical method to increase the testing frequency or frequency of operation. In addition, small errors in physical location cause significant errors in calibration, errors in response due to external perturbations, and shifts in response due to electrical currents caused by the flu lines saturating the entire device during testing.
The current state of the art row level or slider level test is running in the low kHz range and many of the commonly available external testers operate at pseudo DC data rates.
A typical prior-art tester for measuring the resistive properties of a magnetoresistive element 11 as a function of applied magnetic field B is illustrated in FIG. 2. The prior-art tester includes an electromagnet 12, to which a DC current is applied by a controllable power supply 14. The power supply 14 supplies current to the magnet 12 in an alternating or patterned fashion, as shown in the graph 16. Each step changes the value of the applied magnetic field B.
The magnetoresistive element 11 is placed in the magnetic field created by the electromagnet 12 and a bias current 18 is applied to it. The bias current 18 (ibias) is usually given a value typical of that anticipated during use of the head in a disk drive or other data storage medium. The magnetoresistive element 11 is shown as two separate resistances 20 and 22. Resistance 20 represents the no magnetic field or background resistance R which does not vary as a function of B, while variable resistance 22 represents the much smaller resistance r which varies as a function of the applied magnetic field B and which is the quantity of interest for most applications of magnetoresistive heads. As illustrated in FIG. 1, values for r are taken to be positive, so that the total resistance of the magnetoresistive element 11 is given by Rtotal=Rxe2x88x92r(B).
The device illustrated in FIG. 2 includes a resistance measuring device 24 which measures Rtotal as a function of the magnetic field B applied by the magnet 12 at each value of the current provided to the magnet 12 by the power supply 14. The resistance measuring device 24 is usually chosen to be a resistance bridge which is balanced to obtain the value of Rtotal each time the magnetic field B is changed by the power supply 14.
According to one embodiment, an additional structure is integrated into the design and manufacture of a magnetic head that allows self-generation of magnetic fields from within the head. This structure, being small in physical size and in close proximity to the reader portion of the head, allows for testing at data rates well beyond the capability of existing testers. Today""s state of the art magnetic recording head testers are limited to operational frequencies in the kHz range. Embodiments of the present invention allow operation into the multiple megahertz range.
The device includes a conductor or conductors placed in close proximity to the read portion of a magnetic recording head and connected to an externally accessible connection. A high frequency signal is passed through the conductor to generate a magnetic field through the read device and simulate, for example, the head crossing magnetic domains on a magnetic memory disk. With the ability to control the size and placement of the conductor, the field generated is proportional to the applied current waveform. Further, the device can be constructed in a fashion that allows disablement of the conductor by laser ablation, mechanical cutting, electrical overcurrent, etc. if desired.
Thus, the embodiments presented herein provide a structure added to a magnetic head at extremely low cost using existing manufacturing techniques, and provide a very high data rate test capability in a controlled environment.